Add page about setting raw HTML content (denoland#2189)

docs/latest/examples/rendering-raw-html.md

@@ -0,0 +1,81 @@
+---
+description: |
+  How to render raw HTML in Fresh.
+---
+
+Text content in Fresh is always escaped, whether serverside rendered or rendered 
+in islands. While this generally desired, it can create issues in certain 
+situations.
+
+## Warning
+
+The TL;DR is to use Preact's `dangerouslySetInnerHTML`. As the name implies,
+it should not be used lightly.
+
+Setting arbitrary HTML can be dangerous. Make sure you trust the source.
+Rendering user-supplied HTML to the DOM makes your site vulnerable to cross-
+site scripting. The markup must first be sanitizied, or better
+yet, something you trust.
+
+## Example: Rendering JSON-LD
+
+Suppose we need to add some microdata markup to a page. The following will
+result in **escaped charaters, and will not work**:
+
+```tsx
+const json = `
+{
+  "@context": "http://schema.org",
+  "@type": "PostalAddress",
+  "streetAddress": "8888 University Drive",
+  "addressLocality": "Burnaby",
+  "addressRegion": "British Columbia"
+`;
+
+export default function JsonLd() {
+  return (
+    <script type="application/ld+json">{json}</script>
+  );
+}
+```
+
+Instead, we can use `dangerouslySetInnerHTML`:
+
+```tsx
+export default function JsonLd() {
+  return (
+    <script type="application/ld+json"
+      dangerouslySetInnerHTML={{ __html: json }}
+    />
+  );
+}
+```
+
+## Another example: Code highlighting
+
+Syntax highlighers parse strings into HTML tags, allowing them to be 
+individually styled with CSS. We can build a simple Preact syntax highligher
+like so:
+
+```tsx
+import Prism from "https://esm.sh/prismjs@1.29.0";
+
+interface Props {
+  code: string;
+  lang: string;
+}
+
+export default function Code({ code, lang }: Props) {
+  const parsed = Prism.highlight(code, Prism.languages[lang], lang);
+
+  return (
+    <pre data-lang={lang} className={`language-${lang}`}>
+      <code dangerouslySetInnerHTML={{
+        __html: parsed
+      }} />
+    </pre>
+  );
+}
+```
+
+Of course, we will also have to add some CSS to make this look nice.

docs/toc.ts

@@ -90,6 +90,7 @@ const toc: RawTableOfContents = {
           ["creating-a-crud-api", "Creating a CRUD API", "link:latest"],
           ["handling-complex-routes", "Handling complex routes", "link:latest"],
           ["rendering-markdown", "Rendering markdown", "link:latest"],
+          ["rendering-raw-html", "Rendering raw HTML", "link:latest"],
           [
             "sharing-state-between-islands",
             "Sharing state between islands",
@@ -160,6 +161,7 @@ const toc: RawTableOfContents = {
           ["creating-a-crud-api", "Creating a CRUD API"],
           ["handling-complex-routes", "Handling complex routes"],
           ["rendering-markdown", "Rendering markdown"],
+          ["rendering-raw-html", "Rendering raw HTML"],
           ["sharing-state-between-islands", "Sharing state between islands"],
           ["using-csp", "Using CSP"],
           ["active-links", "Styling active links"],